1. Field of the Invention
The present invention relates in general to the art of guiding a light beam in a light conducting medium and, in particular, to a structure inside a light conducting medium directing the light beam along a predetermined path.
2. Background Art
Visible light beams, such as lasers, are often used in various procedures involving imaging equipment to locate a point of entry and an angle of approach to a subsurface target, such as a tumor or any other area inside the body of a patient. In these procedures a visible light beam usually serves as a visible guide for accessing the subsurface target with an invasive instrument which is maintained in an aligned position with the light beam. In computer tomography or fluoroscopically guided procedures imaging is used to localize and determine the position of a subsurface target requiring treatment or medical investigation. Once the position of a subsurface target is determined, a doctor then uses the imaging equipment to select the desired path of access to the subsurface target with invasive instruments such as needles, drainage catheters, localization wires or other biopsy tools to perform necessary procedures. After the desired path is selected, the doctor guides the invasive instrument along the path to the target by maintaining the invasive instrument in alignment with that selected path.
As a practical matter, constantly maintaining the invasive instrument in alignment with the selected path during a medical procedure may be difficult. A solution to the alignment maintenance problem is disclosed in patent application Ser. No. 08/859,380 "Energy Guided Apparatus And Method With Indication of Alignment", which application is incorporated herein by reference. Described in that application is a visible light beam, such as a laser beam, directed along a predetermined path at a preselected target within a patient's body, therefore illuminating the path and making it visible to a doctor. The invasive instrument described in that application has a light conducting channel that allows the light beam to enter the instrument through an opening and propagate inside the light conducting channel. If the light beam and the invasive instrument are properly aligned, the light beam travels through the channel and reaches a sensor which indicates the alignment by dispersing visible light or by any other means suitable for a particular application.
The accuracy of alignment of the visible light beam and the invasive instrument is important for performing a medical procedure correctly, precisely and efficiently. Given a very high energy concentration of laser beams that are commonly employed in medicine, a non-aligned laser beam reflected from the interior surfaces of the light conducting channel of the invasive instrument can still reach the sensor and falsely indicate alignment between the invasive instrument and the focused laser beam. This, in turn, greatly degrades the accuracy of alignment of the laser beam and the instrument and results in incorrect performance of a medical procedure. For example, a 5 mW laser focused to a 1 mm spot at a distance of 750 mm from the laser source has a visible light intensity equivalent to the light intensity of a 35,000 W bulb viewed at 750 mm. As a result, such an intense non-aligned laser beam can be reflected from the interior surfaces of the conducting channel and falsely indicate alignment of the invasive instrument and the focused laser beam.
Therefore, a need exists to have an invasive instrument with such an improved light conducting channel that will reduce the probability that a nonaligned visible light beam gets reflected from the interior surface of the channel and causes a false indication of alignment after reaching and illuminating the sensor.